Color control by alteration of wavelength converting element

ABSTRACT

A light emitting device is produced by depositing a layer of wavelength converting material over the light emitting device, testing the device to determine the wavelength spectrum produced and correcting the wavelength converting member to produce the desired wavelength spectrum. The wavelength converting member may be corrected by reducing or increasing the amount of wavelength converting material. In one embodiment, the amount of wavelength converting material in the wavelength converting member is reduced, e.g., through laser ablation or etching, to produce the desired wavelength spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division U.S. application Ser. No. 12/277,230, filed Nov. 24,2008, now U.S. Pat. No. 7,902,566, which is a division of U.S.application Ser. No. 11/444,592, filed May 31, 2006, now U.S. Pat. No.7,462,502, entitled “Color Control by Alteration of WavelengthConverting Element” which is a continuation-in-part of and claimspriority to U.S. patent application Ser. No. 10/987,241, filed Nov. 12,2004, now U.S. Pat. No. 7,419,839, entitled “Bonding an Optical Elementto a Light Emitting Device”, by Michael D. Camras et al. U.S. Pat. Nos.7,902,566, 7,462,502, and 7,419,839 are all incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to light emitting devices and,more particularly, to controlling the color consistency of lightemitting devices that use wavelength converting members.

BACKGROUND

There has been a long term need for precise color control ofsemiconductor light emitting devices, such as light emitting diodes,that produce “white” light. A common method of making a packaged lightemitting device that emits white light is to employ a phosphor (oftenYAG based) and a blue LED chip. The combination of blue light from theLED and “yellow” light from the phosphor makes “white” light.Unfortunately this approach results in a large spread in the “color” ofwhite light both in terms of correlated color temperature (CCT) and inproximity to the blackbody curve. The color control of phosphorconverted LEDs sold today has a range of at least around 2000K to 3000Kfor white parts with the correlated color temperature (CCT) varying from5500K to 8500K. Discernable color differences are dependent on the colortemperature of the LED and at 6500K, differences as small as 300K areapparent to the viewer. The color control of standard lighting sources,such as fluorescent bulbs, has color temperature variations much lessthan this and color differences are usually not discernable to theviewer. Although phosphor converted LEDs have been commerciallyavailable for more than 5 years, and some improvements have been made,the color temperature still varies too much to be acceptable to mostpotential customers and applications.

SUMMARY

In accordance with one embodiment of the present invention, a layer ofwavelength converting material is deposited over a light emittingelement, the wavelength spectrum produced by the combination of thewavelength converting material and the light emitting element isdetermined, and the wavelength converting material is corrected byaltering the amount of wavelength converting material in the wavelengthconverting member to produce the desired wavelength spectrum. Thewavelength converting member may be corrected by reducing or increasingthe amount of wavelength converting material. In one embodiment, amountof wavelength converting material is reduced, e.g., through laserablation or etching, to produce the desired wavelength spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a side view of an LED die mounted on a submount andan optical element that is to be bonded to the LED die.

FIG. 1B illustrates the optical element bonded to the LED die.

FIG. 1C illustrates a wavelength converting member bonded to the LEDdie.

FIG. 2 illustrates an embodiment in which multiple LED dice are mountedto a submount and a separate optical element is bonded to each LED die.

FIG. 3 illustrates an embodiment in which multiple LED dice are mountedto a submount and a single optical element with a wavelength convertinglayer is bonded to the LED dice.

FIG. 4 is a flow chart of one implementation of producing such an LEDdevice with wavelength converting material covering the optical element.

FIG. 5 illustrates an embodiment in which a layer of wavelengthconverting material is disposed between the bonding layer and theoptical element.

FIG. 6 illustrates an embodiment in which a layer of wavelengthconverting material is deposited on the LED die.

FIG. 7 illustrates an array of LEDs, which are mounted on a board.

FIG. 8 is a graph of the broad spectrum produced by a phosphor convertedblue LED.

FIG. 9 is a CIE chromaticity diagram with a point marked for thespectrum shown in FIG. 8.

FIG. 10 is a graph of the spectra produced by phosphor converted LEDsand colored LEDs, which are combined to produce an approximatelycontinuous spectrum.

FIG. 11 is the color space that shows the variation in the CCT that maybe produced by varying the brightness of the colored LEDs.

FIG. 12 is the color space that illustrates variable CCT values for anarray of 29 phosphor converted LEDs and 12 color LEDs.

FIGS. 13A, 13B, and 13C illustrate top plan views and FIGS. 14A, 14B,and 14C illustrate side views of an embodiment of producing an LEDdevice that emits light with a desired correlated color temperature.

FIGS. 15A, 15B, and 15C illustrate top plan views of a device similar tothe device shown in FIG. 13C, but with the wavelength converting memberablated as a series of holes.

FIG. 16 is the color space showing the change in the CCT of LED devicesduring laser ablation of the wavelength converting members.

DETAILED DESCRIPTION

FIG. 1A illustrates a side view of a transparent optical element 102 anda light emitting diode (LED) die 104 that is mounted on a submount 106.The optical element 102 can be bonded to the LED die 104 in accordancewith an embodiment of the present invention. FIG. 1B illustrates theoptical element 102 bonded to the LED die 104.

The term “transparent” is used herein to indicate that the element sodescribed, such as a “transparent optical element,” transmits light atthe emission wavelengths of the LED with less than about 50%, preferablyless than about 10%, single pass loss due to absorption or scattering.The emission wavelengths of the LED may lie in the infrared, visible, orultraviolet regions of the electromagnetic spectrum. One of ordinaryskill in the art will recognize that the conditions “less than 50%single pass loss” and “less than 10% single pass loss” may be met byvarious combinations of transmission path length and absorptionconstant.

LED die 104 illustrated in FIGS. 1A and 1B includes a firstsemiconductor layer 108 of n-type conductivity (n-layer) and a secondsemiconductor layer 110 of p-type conductivity (p-layer). Semiconductorlayers 108 and 110 are electrically coupled to an active region 112.Active region 112 is, for example, a p-n diode junction associated withthe interface of layers 108 and 110. Alternatively, active region 112includes one or more semiconductor layers that are doped n-type orp-type or are undoped. LED die 104 includes an n-contact 114 and ap-contact 116 that are electrically coupled to semiconductor layers 108and 110, respectively. Contact 114 and contact 116 can be disposed onthe same side of LED die 104 in a “flip chip” arrangement. A transparentsuperstrate 118 coupled to the n layer 108 may be formed from a materialsuch as, for example, sapphire, SiC, GaN, GaP, diamond, cubic zirconia(ZrO2), aluminum oxynitride (AlON), AlN, spinel, ZnS, oxide oftellurium, oxide of lead, oxide of tungsten, polycrystalline aluminaoxide (transparent alumina), and ZnO. Alternatively, the substrate orsuperstrate can be removed so that only the layers that are epitaxiallygrown on the substrate or superstrate are present. In one embodiment,the substrate or superstrate is removed after the LED die is mounted tothe submount. This can be accomplished by a wet or dry etch or by alaser lift-off process.

Active region 112 emits light upon application of a suitable voltageacross contacts 114 and 116. In alternative implementations, theconductivity types of layers 108 and 110, together with respectivecontacts 114 and 116, are reversed. That is, layer 108 is a p-typelayer, contact 114 is a p-contact, layer 110 is an n-type layer, andcontact 116 is an n-contact.

Semiconductor layers 108 and 110 and active region 112 may be formedfrom III-V semiconductors including but not limited to AlN, AlP, AlAs,AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, II-VI semiconductorsincluding but not limited to ZnS, ZnSe, CdSe, ZnO, CdTe, group IVsemiconductors including but not limited to Ge, Si, SiC, and mixtures oralloys thereof.

Contacts 114 and 116 are, in one implementation, metal contacts formedfrom metals including but not limited to gold, silver, nickel, aluminum,titanium, chromium, platinum, palladium, rhodium, rhenium, ruthenium,tungsten, and mixtures or alloys thereof.

Although FIGS. 1A and 1B illustrate a particular structure of LED die104, the present invention is independent of the structure of the LEDdie. Accordingly, other types of LED configurations may be used insteadof the specific configuration shown. Further, the number ofsemiconductor layers in LED die 104 and the detailed structure of activeregion 112 may differ. It should be noted that dimensions of the variouselements of LED die 104 illustrated in the various figures are not toscale.

The LED die 104 can be mounted to submount 106 via contacts elements120, such as solder bumps, pads, or other appropriate elements, such asa layer of solder or metal. Contact elements 120 will be sometimesreferred to herein as bumps 120 for the sake of simplicity. Bumps 120are manufactured from Au, Sn, Ag, Sb, Cu, Pb, Bi, Cd, In, Zn or alloysthereof including AuSn, SnSb, SnCu, SnAg, SnAgBi, InSn, BiPbSn, BiPbCd,BiPbIn, InCd, BiPb, BiSn, InAg, BiCd, InBi, InGa, or other appropriatematerial with a melting temperature that is greater than the temperaturethat will be used to bond the optical element 102 to the LED die 104,but is preferably Au or AuSn. In one implementation, the meltingtemperature of bumps 120 is greater than 250° C. and preferably greaterthan 300° C. The submount 106 may be, e.g., silicon, alumina or AlN andmay include vias for backside connections.

The LED die 104 can be mounted to the submount 106, e.g., usingthermosonic bonding. For example, during the thermosonic bondingprocess, the LED die 104 with bumps 120 are aligned with the submount106 in the desired position while the submount 106 is heated toapproximately 150-160° C. A bond force of, e.g., approximately 50-100gm/bump, is applied to the LED die 104 by a bonding tool, whileultrasonic vibration is applied. Other desired processes may be used,such as thermo-compression, to bond the LED die 104 to the submount 106.As is well known in the art, with thermo-compression higher temperaturesand greater bonding forces are typically required than for an ultrasonicattachment.

In some embodiments, an underfill may be used with the LED die 104 andsubmount 106. The underfill material may have good thermal conductivityand have a coefficient of thermal expansion that approximately matchesthe LED die 104 and the submount 106. The underfill may also be used toblock light emitted from the side of the die. In another embodiment, aprotective side coat, e.g., of silicone or other appropriate material,may be applied to the sides of the LED die 104 and the submount 106. Theprotective side coating acts as a sealant and limits exposure of the LED104 and the bumps 120 to contamination and the environment. Theprotective side coating can also have optical properties such aspreventing an undesired color light from being emitted, converting theundesired light into a desired color, or recycling the undesired lightback into the chip for a second chance to exit as the desired color.

For more information regarding producing bumps 120 from Au or Au/Sn andfor submounts with backside vias and bonding LED dice with Au or Au/Snbumps to a submount, see U.S. Ser. No. 10/840,459, by Ashim S. Hague,filed May 5, 2004, which has the same assignee as the present disclosureand is incorporated herein by reference. It should be understood,however, that the present invention is not limited to any specific typeof submount and that any desired submount configuration and any desiredcontact element may be used if desired. In some applications, forexample, a contact pad may be desirable.

In one embodiment, after the LED die 104 is mounted to the submount 106,the optical element 102 is thermally bonded to the LED die 104. A layerof bonding material can be applied to the bottom surface of the opticalelement 102 to form transparent bonding layer 122 that is used to bondoptical element 102 to LED die 104. In some embodiments, the transparentbonding layer 122 may be applied to the top surface of the LED die 104,e.g., to superstrate 118, (as indicated by the dotted lines 122′ in FIG.1A). If the superstrate 118 is removed, bonding layer 122′ may beapplied to semiconductor layer 108. The bonding layer 122′ can beapplied to the LED die 104 prior to or after mounting the LED die 104 tothe submount 106. Alternatively, no bonding layer may be used and theoptical element 102 may be bonded directly to the LED die 104, e.g., thesuperstrate 118 or layer 108 if the superstrate 118 is removed. Thetransparent bonding layer 122 is, for example, about 10 Angstroms (Å) toabout 100 microns (μm) thick, and is preferably about 1000 Å to about 10μm thick, and more specifically, about 0.5 μm to about 5 μm thick. Thebonding material is applied, for example, by conventional depositiontechniques including but not limited to spin coating, spraying,sputtering, evaporation, chemical vapor deposition (CVD), or materialgrowth by, for example, metal-organic chemical vapor deposition (MOCVD),vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), or molecular beamepitaxy (MBE), or by dispensing a liquid resin, organic and/orinorganic, that acts as the bonding agent. Other bonding methods arealso possible, such as the use of UV cured adhesives. In one embodiment,the optical element 102 may be covered with a wavelength convertingmaterial 124, which will be discussed in more detail below. In anotherembodiment, such as illustrated in FIG. 1C, a wavelength convertingmaterial 124′ is bonded to the LED die 104 without an interveningoptical element 102 and bonding layer 122. If desired, a bonding layer122 may be used with the wavelength converting material 124′. In someembodiments, the surface of the wavelength converting material 124′and/or the surface of the LED 104, superstrate 118 or semiconductorlayer 108, if superstrate 118 is removed, is patterned or roughened,e.g. using ablation, sawing, and/or other means such as wet or dryetching with or without lithography, to frustrate TIR and to increasethe proportion of light that escapes and/or imparts some useful beamshaping quality to the emission cone.

In one implementation, the transparent bonding layer 122 is formed froma glass bonding material such as SF59, LaSF 3, LaSF N18, SLAH51, LAF10,NZK7, NLAF21, LASFN35, SLAM60, or mixtures thereof, which are availablefrom manufactures such as Schott Glass Technologies Incorporated, ofDuryea, Pa. and Ohara Corporation in Somerville, N.J. Bonding layer 122may also be formed from a high index glass, such as(Ge,As,Sb,Ga)(S,Se,Te,Cl,I,Br) chalcogenide or chalcogen-halogenideglasses, for example. If desired, lower index materials, such as glassand polymers may be used. Both high and low index resins, for example,silicone or siloxane available from manufactures such as Shin-EtsuChemical Co., Ltd., Tokyo, Japan. The side chains of the siloxanebackbone may be modified to change the refractive index of the silicone.

In other implementations, bonding layer 122 may be formed from III-Vsemiconductors including but not limited to GaP, InGaP, GaAs, and GaN;II-VI semiconductors including but not limited to ZnS, ZnSe, ZnTe, CdS,CdSe, and CdTe; group IV semiconductors and compounds including but notlimited to Si, and Ge; organic semiconductors, metal oxides includingbut not limited to oxides of antimony, bismuth, boron, copper, niobium,tungsten, titanium, nickel, lead, tellurium, phosphor, potassium,sodium, lithium, zinc, zirconium, indium tin, or chromium; metalfluorides including but not limited to magnesium fluoride, calciumfluoride, potassium fluoride, sodium fluoride, and zinc fluoride; metalsincluding but not limited to Zn, In, Mg, and Sn; yttrium aluminum garnet(YAG), phosphide compounds, arsenide compounds, antimonide compounds,nitride compounds, high index organic compounds; and mixtures or alloysthereof.

In some embodiments, the transparent bonding layer 122 may be applied tothe top surface of the LED die 104, e.g., to superstrate 118, (asindicated by dotted lines 122′ in FIG. 1A). The bonding layer 122′ canbe applied to the LED die 104 prior to mounting the LED die 104 to thesubmount 106. Alternatively, no bonding layer may be used and theoptical element 102 may be bonded directly to the LED die 104, e.g., thesuperstrate 118 or layer 108 if the substrate is removed. Inimplementations where the LED die 104 is configured with the n-contactand p-contact on opposite sides of the die 104, the transparent bondinglayer 122 or 122′ may be patterned with, for example, conventionalphotolithographic and etching techniques to leave the top contactuncovered by bonding material and thus to permit electrical contact witha metallization layer on the optical element 102, which may serve as alead, as is described in U.S. Ser. No. 09/880,204, filed Jun. 12, 2001,by Michael D. Camras et al., entitled “Light Emitting Diodes withImproved Light Extraction Efficiency” having Pub. No. 2002/0030194,which is incorporated herein by reference.

In one implementation, the optical element 102 is formed from opticalglass, high index glass, GaP, CZ, ZnS, SiC, sapphire, diamond, cubiczirconia (ZrO2), AlON, by Sienna Technologies, Inc., polycrystallinealuminum oxide (transparent alumina), spinel, Schott glass LaFN21,Schott glass LaSFN35, LaF2, LaF3, and LaF10 available from OptimaxSystems Inc. of Ontario, N.Y., an oxide of Pb, Te, Zn, Ga, Sb, Cu, Ca,P, La, Nb, or W, or any of the materials listed above for use as bondingmaterials in transparent bonding layer 122, excluding thick layers ofthe metals.

The transparent optical element 102 may have a shape and a size suchthat light entering optical element 102 from LED die 104 will intersectsurface 102 a of optical element 102 at angles of incidence near normalincidence. Total internal reflection at the interface of surface 102 aand the ambient medium, typically air, is thereby reduced. In addition,since the range of angles of incidence is narrow, Fresnel reflectionlosses at surface 102 a can be reduced by applying a conventionalantireflection coating to the surface 102 a. The shape of opticalelement 102 is, for example, a portion of a sphere such as a hemisphere,a Weierstrass sphere (truncated sphere), or a portion of a sphere lessthan a hemisphere. Alternatively, the shape of optical element 102 is aportion of an ellipsoid such as a truncated ellipsoid, a side emitter ormay be elongated in shape to accommodate a LED array or rectangular LEDsas described in US 2005/0023545, by the same assignee and which isincorporated herein by reference. The angles of incidence at surface 102a for light entering optical element 102 from LED die 104 more closelyapproach normal incidence as the size of optical element 102 isincreased. Accordingly, the smallest ratio of a length of the base oftransparent optical element 102 to a length of the surface of LED die104 is preferably greater than about 1, more preferably greater thanabout 2.

After the LED die 104 is mounted on the submount 106, the opticalelement 102 can be thermally bonded to the LED die 104. For example, tobond the optical element 102 to the LED die 104, the temperature ofbonding layer 122 is raised to a temperature between about roomtemperature and the melting temperature of the contact elements 120,e.g., between approximately 150° C. to 450° C., and more particularlybetween about 200° C. and 400° C., and optical element 102 and LED die104 are pressed together at the bonding temperature for a period of timeof about one second to about 6 hours, preferably for about 30 seconds toabout 30 minutes, at a pressure of about 1 pound per square inch (psi)to about 6000 psi. By way of example, a pressure of about 700 psi toabout 3000 psi may be applied for between about 3 to 15 minutes. Ifdesired, other bonding processes may be used.

The thermal bonding of the optical element 102 to the LED die 104requires the application of elevated temperatures. With the use ofcontact elements 120 that have a high melting point, i.e., higher thanthe elevated temperature used in the thermal bonding process, the LEDdie 104 may be mounted to the submount 106 before the optical element102 is bonded to the LED die 104 without damaging the LED die/submountconnection. Mounting the LED die 104 to the submount 106 prior tobonding the optical element 102 simplifies the pick and place process.

Bonding an optical element 102 to an LED die 104 is described in US Pub.No. 2002/0030194; 2005/0032257; Ser. No. 09/660,317, filed Sep. 12,2000, by Michael D. Camras et al., entitled “Light Emitting Diodes withImproved Light Extraction Efficiency”; U.S. Pat. Nos. 6,987,613; or7,009,213, all of which have the same assignee as the presentapplication and which are incorporated herein by reference. Further, theprocess of bonding optical element 102 to LED die 104 described abovemay be performed with devices disclosed in U.S. Pat. Nos. 5,502,316 and5,376,580, incorporated herein by reference, previously used to bondsemiconductor wafers to each other at elevated temperatures andpressures. The disclosed devices may be modified to accommodate LED diceand optical elements, as necessary. Alternatively, the bonding processdescribed above may be performed with a conventional vertical press. Inone embodiment, a mass bonding process can be performed with manydevices at once in an oven, with or without pressure.

It should be noted that due to the thermal bonding process, a mismatchbetween the coefficient of thermal expansion (CTE) of optical element102 and LED die 104 can cause optical element 102 to delaminate ordetach from LED die 104 upon heating or cooling. Accordingly, opticalelement 102 should be formed from a material having a CTE thatapproximately matches the CTE of LED die 104. Approximately matching theCTEs additionally reduces the stress induced in the LED die 104 bybonding layer 122 and optical element 102. With suitable CTE matching,thermal expansion does not limit the size of the LED die that may bebonded to the optical element and, thus, the optical element 102 may bebonded to a large LED die 104, e.g., up to 1 mm², up to 2 mm², up to 4mm², up to 9 mm², up to 16 mm², or larger than 16 mm².

FIG. 2 illustrates an embodiment in which multiple LED dice 204 a, 204b, and 204 c (sometimes collectively referred to as LED dice 204) aremounted on a submount 206. The LED dice 204 are schematicallyillustrated in FIG. 2 without showing the specific semiconductor layers.Nevertheless, it should be understood that the LED dice 204 may besimilar to LED die 104 discussed above.

The LED dice 204 are each mounted to submount 206 as described above.Once the LED dice 204 are mounted on submount 206, individual opticalelements 202 a, 202 b, and 202 c can be bonded to LED dice 204 a, 204 b,and 204 c, respectively, in a manner such as that described above.

If desired, the LED dice 204 may be the same type of LED and may producethe same wavelengths of light. In another implementation, one or more ofthe LED dice 204 may produce different wavelengths of light, which whencombined may be used to produce light with a desired correlated colortemperature (CCT), e.g., white light. Another optical element (not shownin FIG. 2) may be used to cover optical elements 202 a, 202 b, and 202 cand aid in mixing the light.

FIG. 3 illustrates an embodiment of an LED device 300 that includesmultiple LED dice 304 a, 304 b, and 304 c (sometimes collectivelyreferred to as LED dice 304) mounted on a submount 306 and a singleoptical element 302 bonded to the LED dice 304. The LED dice 304 may besimilar to LED die 104 discussed above.

The use of a single optical element 302 with multiple LED dice 304, asshown in FIG. 3, is advantageous as the LED dice 304 can be mountedclose together on submount 306. Optical components typically have alarger footprint than an LED die to which it is bonded, and thus, theplacement of LED dice with separate optical elements may be constrainedby the size of the optical elements.

After the LED dice 304 are mounted to the submount, there may be slightheight variations in the top surfaces of the LED dice 304, e.g., due tothe differences in the height of the contact elements 320 and thicknessof the dice. When the single optical element 302 is thermally bonded tothe LED dice 304, any differences in the height of the LED dice 304 maybe accommodated by the compliance of the contact elements 320.

During the thermal bonding process of the optical element 302 to the LEDdice 304, the LED dice 304 may shift laterally due to the heating andcooling of the submount 306. With the use of some contact elements 320,such as Au, the compliance of the contact elements 320 can be inadequateto accommodate lateral shift of the LED dice 304. Accordingly, thecoefficient of thermal expansion of the optical element 302 (CTE₃₀₂)should approximately match the coefficient of thermal expansion of thesubmount 306 (CTE₃₀₆). With an approximate match between CTE₃₀₂ andCTE₃₀₆ any movement of the LED dice 304 caused by the expansion andcontraction of the submount 306 will be approximately matched by theexpansion and contraction of the optical element 302. A mismatch betweenCTE₃₀₂ and CTE₃₀₆, on the other hand, can result in the delamination ordetachment of the LED dice 304 from the optical element 302 or otherstress induced damage to the LED device 300, during the heating andcooling of the thermal bonding process.

With the use of sufficiently small LED dice 304, the thermal expansionof the LED dice 304 themselves during the thermal bonding process may beminimized. With the use of large LED dice 304, however, the amount ofthermal expansion of the LED dice 304 during the thermal bonding processmay be large and thus, the CTE for the LED dice 304 also should beappropriately matched to approximately the CTE of the submount 306 andthe optical element 302.

The LED dice 304 may be, e.g., InGaN, AlInGaP, or a combination of InGaNand AlInGaP devices. In one implementation, the submount 302 may bemanufactured from AlN, while the optical element 302 may be manufacturedfrom, e.g., SLAM60 by Ohara Corporation, or NZK7 available from SchottGlass Technologies Incorporated. In another implementation, an Aluminasubmount 306 may be used along with an optical element 302 manufacturedfrom sapphire, Ohara Glass SLAH51 or Schott glass NLAF21. In someimplementations, a bulk filler 305 between the LED dice 304 and thesubmount 306 may be used. The bulk filler 305 may be, e.g., epoxy,silicone, or glass. The bulk filler 305 may have good thermalconductivity and may approximately match the CTE of the submount 306 andthe dice 304. If desired, a protective side coating may be appliedalternatively or in addition to the bulk filler 305. This protectiveside coating may be used to block side light from the die.

In one implementation, all of the LED dice 304 may be the same type andproduce different or approximately the same wavelengths of light.Alternatively, with an appropriate choice of LED dice 304 and/orwavelength conversion materials, different wavelengths of light may beproduced, e.g., blue, green and red. When LED dice 304 are the sametype, the CTE for the LED dice 304 will be approximately the same. Itmay be desirable for the CTE of the LED dice 304 to closely match thecoefficient of thermal expansion of the optical element 302 and thesubmount 306 to minimize the risk of delamination or detachment orstress induced damage to the LED device 300 during the thermal bondingprocess. An example of approximately CTE matched device 300 wouldconsist of LED dice 304 containing a sapphire substrate, a sapphire orapproximately CTE matched glass optical element 302, and an aluminasubmount 306. The degree of CTE matching can depend on parameters suchas the compliance of the bonding materials, the temperature range thatthe device is bonded, processed, or operated and the bond area size. Insome embodiments, CTE mismatch should be less than 10%. In otherembodiments, a CTE mismatch of greater than 10% may be acceptable andalso result in a reliable device.

In another implementation, the LED dice 304 may be different types andproduce different wavelengths of light. With the use of different typesof LED dice, the CTE of the dice can vary making it difficult to matchthe CTE for all the LED dice 304 with that of the optical element 302and the submount 306. Nevertheless, with a judicious choice of theoptical element 302 and submount 306 with CTEs that are as close aspossible to that of the LED dice 304, problems associated withdetachment of the LED dice 304 or other damage to the device 300 duringthe thermal bonding process may be minimized. Additionally, with the useof relatively small LED dice 304, e.g., the area smaller thanapproximately 1 mm², problems associated with thermal bonding a singleoptical element 302 to multiple dice 304 may also be reduced. The use ofa bulk filler 305 may also prevent damage to the device during thermalprocessing or operation.

As shown in FIG. 3, in one implementation, the optical element 302 maybe coated with a wavelength converting material to form wavelengthconverting member 310, such as a phosphor coating. In one embodiment,the wavelength converting material is YAG. Of course there are manyvariants of YAG and non-YAG phosphors that could be used if desired.Alternatively, multiple layers of different phosphors may be used, suchas red and green phosphors that are used with a blue LED. FIG. 4 is aflow chart of one implementation of producing such a device. Asillustrated in FIG. 4, the LED dice 304 are mounted to the submount 306(step 402) and the optical element 302 is bonded to the LED dice 304(step 404). After the optical element 302 is bonded to the LED dice 304,a layer of the wavelength converting material is deposited over theoptical element 302 (step 406) to form a wavelength converting member310. The device can then be tested, e.g., by applying a voltage acrossthe active regions of the LED dice 304 and detecting the wavelengthspectrum of light produced by the device (step 408). If the device doesnot produce the desired wavelength spectrum (step 410), the thickness ofthe wavelength converting member 310 is altered (step 411), e.g., bydepositing additional wavelength converting material over the opticalelement 302 or by removing some of the wavelength converting material byablation, etching or dissolution and the device is again tested (step408). The process stops once the desired wavelength spectrum of light isproduced (step 412). The wavelength spectrum of the device determinesthe CCT and its proximity to the plankian. Hence, it should beunderstood that a desired CCT range or a desired CCT range and itsdesired proximity to the plankian can determine the desired wavelengthspectrum of light produced by the device.

Thus, the thickness of the wavelength converting member 310 coating iscontrolled in response to the light produced by the LED dice 304resulting in a highly reproducible correlated color temperature.Moreover, because the deposition of the wavelength converting materialis in response to the specific wavelengths produced by the LED dice 304,a variation in the wavelengths of light produced by LED dice 304 can beaccommodated. Accordingly, fewer LED dice 304 will be rejected forproducing light with an undesirable wavelength spectrum.

Although FIG. 4 is described for the embodiment shown in FIG. 3, itshould be understood that the process of correcting the wavelengthconverting member 310 as shown in FIG. 4 may be applied to theembodiments shown in FIGS. 1B, 1C, and 2 as well. That is, wavelengthconverting member 124 in FIG. 1B, and wavelength converting members (notshown) on 202 a, 202 b, 202 c in FIG. 2 can be corrected by the processof FIG. 4. Moreover, wavelength converting member 124′ in FIG. 1C can becorrected by a similar process to that shown in FIG. 4, except that thewavelength converting material is applied to the LED die 104 without theintervening optical element. Also in another embodiment, the LED dice donot need to be mounted to a submount for the wavelength spectrumaltering process. Other LED configurations and packaging may be used ifdesired.

FIGS. 13A, 13B, and 13C illustrate top plan views and FIGS. 14A, 14B,and 14C illustrate side views of an embodiment of producing an LEDdevice that emits light with a desired correlated color temperature. Alight emitting element, for example, LED die 802 in FIGS. 13A and 14A,is produced and mounted on a submount 804, along with an electrostaticdischarge circuit (ESD) 806, such as a Zener diode. The LED die 802 maybe produced and mounted to the submount 804 as described herein or ifdesired, other manufacturing and packaging processes may be used. Forexample, in some embodiments, a submount 804 need not be used.Alternatively, a lens or dome may be mounted over the LED die 802, suchas that illustrated in FIG. 1A.

The light emitting element, for example, LED die 802 (or dome if used)is then coated with a wavelength converting material to form awavelength converting member 808 as illustrated in FIGS. 13B and 14B toproduce a light emitting device. For the sake of simplicity, the entiredevice including the submount 804 and the ESD circuit 806 may be coveredwith the wavelength converting member 808. A coating of wavelengthconverting material may be any of the types described herein and may be,e.g., a coating that is electrophoretically deposited (EPD). The coatingof wavelength converting material can be infused with silicone, sol-gel,siloxane or any suitable resin, which may be cured.

Other types of wavelength converting members 808 and/or depositiontechniques may be used if desired. For example, in one embodiment, thewavelength converting member 808 may be a phosphor spray coated layerinstead of an EPD layer. Alternatively, dispense-jetting, could be usedto deposit the wavelength converting member 808. Dispense-jetting issimilar to ink jetting but with larger drops that carry more material,which can be controlled in precise quantities and locations. Thephosphor may be added to a resin, solvent, hardener, and/or thixotrophicagent. The viscosity and spray pattern may be adjusted to produce thedesired coating of wavelength converting material. Moreover, theindividual devices or submounts containing many devices can be rotatedor otherwise moved during spraying to aid in coating uniformity. Thespray gun can also move during coating. In another embodiment, thewavelength converting member material may be a light converting ceramicthat is bonded to the die or disposed above the die. By way of example,a suitable light converting ceramic that may be used with the presentinvention is described in U.S. Pub. No. 2005/0269582, which has the sameassignee as the present disclosure and is incorporated herein byreference. It may be preferable for a light converting ceramic to be thelast optical element, i.e., there are no additional lens orencapsulation. A light converting ceramic may be ablated, e.g., using ashort wavelength excimer laser.

The combination of the light converted by wavelength converting member808 and the light emitted by the LED die 802 that leaks through thewavelength converting member 808 determines the specific wavelengthspectrum produced by the light emitting device, i.e., the CCT. In oneembodiment the wavelength converting member 808 is deposited on the LEDdie 802 too thick to produce the desired CCT. This allows the CCT of thedevice to be measured or tested and the wavelength converting member 808to be corrected, i.e., wavelength converting material from thewavelength converting member 808 is removed in a controlled fashion toproduce the desired CCT. Alternatively, the wavelength converting membermay be deposited too thin to produce the desired CCT and additionalwavelength converting material is added in a controlled fashion toproduce the desired CCT.

Thus, once the wavelength converting member 808 is deposited, the lightemitting device is tested and the CCT of the emitted light is measured.This process can be performed on individual devices, but throughputwould be increased by performing this process in batches. This can beaccomplished prior to singulating the LED devices or prior tosingulating the submount.

In one embodiment, a computer controlled laser trimming process is usedto ablate the wavelength converting member 808 to generate a correctedwavelength converting member 808 that produces the desired CCT. Wherethe LED devices are tested in batches, the computer controlled laser canablate the wavelength converting member on each LED device by an amountspecifically tailored for that device depending on the individual CCTfor that device.

In one embodiment, the LED device may be tested and the wavelengthconverting member removed in an iterative process, such as thatdescribed in FIG. 4. In another embodiment, once the system iscalibrated, i.e., the amount of wavelength converting material that mustbe removed to produce a specific change in CCT is known, the LED devicecan be measured once and the appropriate amount of material is removedfrom the wavelength converting member. Depending on the amount ofmaterial to be removed, it may be necessary to ablate the wavelengthconverting material using multiple passes, where each pass only removesa small amount of material. The use of multiple passes reduces the riskof charring the resin in the wavelength converting material if it isremoved with a laser. With the use of a light converting ceramic, thereis no resin and thus, it is less likely to char, but it can be moredifficult to ablate.

FIGS. 13C and 14C illustrate the wavelength converting member 808 afterbeing laser ablated. As illustrated in FIG. 13C, a series of lines 8081and spaces 808 s may be used to alter the thickness of the wavelengthconverting member 808, e.g., the amount of wavelength convertingmaterial over the LED die 802 is reduced. In one embodiment, thereduction of the thickness may be over a localized area as opposed tothe entire die. In one embodiment, there may be a reduction in thicknessat one location and an increase in thickness at another location on thesame die. It should be understood that the lines and spaces illustratedin FIG. 13C are illustrative and in practice it may be desirable to usea much smaller pitch. In one embodiment, the wavelength convertingmember 808 is completely removed in localized areas to expose theunderlying LED die 802, thereby forming spaces 808 s. In such anembodiment, the average thickness of the wavelength converting member808 is reduced despite the thickness of the lines 8081 remainingunchanged. The average thickness can be altered, e.g., by increasing thewidth of the spaces and/or or decreasing the width of the lines. Ingeneral, the use of a fine pitch and/or low amplitude is desirable. Inone embodiment, the low amplitude laser ablation may remove only aportion of the thickness of the wavelength converting member 808 suchthat the wavelength converting material in spaces 808 s is thinner thanin the lines 8081, but the underlying LED die 802 is still entirelycovered by the wavelength converting member 808.

Patterns other than lines and spaces may be used to alter the thicknessof the wavelength converting member. For example, FIG. 15A illustrates atop plan view of a device similar to the device shown in FIG. 13C, butwith the wavelength converting member 818 ablated with a series of holes818 h as opposed to lines and spaces. The distance between the holes 818h and/or the radius of the holes 818 h may be varied in order to alterthe average thickness of the wavelength converting member 818 to obtainthe desired CCT. Alternatively, different patterns or the same patternwith different parameters may be used to remove the wavelengthconverting member in localized areas of the LED die 802. For example, aspatial map of the CCT may be generated when the LED device is testedand the CCT of the emitted light is measured. The spatial map of the CCTmay be provided to the computer control and high spots on the coatingmay be ablated, so not only is the desired CCT obtained, but also theCCT is made more spatially uniform. FIG. 15B illustrates an embodimentin which holes 820 h having a smaller radius are located in the centerof the LED die 802 while larger radius holes 818 h are locatedelsewhere. FIG. 15C illustrates an embodiment in which holes 830 areproduced in a specific pattern, which may be, e.g., a design, symbol oremblem. The light source may then be imaged so that the pattern formedby holes 830 is produced having a different color than the surroundinglight.

If desired, processes other than laser ablation may be used to removethe wavelength converting member material. For example, the wavelengthconverting member may be trimmed using other techniques includingmechanical and/or chemical etching, ion beam, or electron beam ablation.

The amount of wavelength converting material removed depends on theinitial CCT and the desired CCT to be obtained. FIG. 16 is a graphillustrating the luminance-chrominance or color space using u′v′coordinates, commonly referred to as u′v′ space, where the line 850 isthe plankian. FIG. 16 illustrates the test results of three differentLED devices with wavelength converting members, which were deposited onthe LED dice, tested, and ablated to alter the wavelength spectrumproduced, which reduces the v′ value and to a lesser extent reduces theu′ value and increases the CCT. The initial u′v′ points of the LEDdevices are shown at the top of the graph. Each data point in FIG. 16illustrates that after each laser ablation, the u′v′ coordinates arefurther decreased. In practice, no further ablation would be performedonce the LED device produces a desired CCT, preferably producing thedesire CCT that is on or near the plankian 850. Thus, the wavelengthspectrum produced by the LED devices is altered until the devicesproduce a point within a desired area of the u′v′ space. As one ofordinary skill in the art will understand, there are many types of spacethat may be used with the present embodiment, including, e.g., xy asshown in FIGS. 9, 11, and 12 or uv space. Thus, the present descriptionof the use of u′v′ space should be understood to include all other typesof space as u′v′ space can be easily transformed into another type ofspace and vice versa.

In FIG. 16, the ablation was performed in small successive steps, i.e.,the pitch was not altered and a small amount of material was removed ateach pass, to illustrate how fine the tuning can be. In a productionenvironment, it may be desirable to use fewer ablation/measurementcycles. However, if too much material is ablated in a single pass, thebinder is more likely to char.

In another implementation, the coating of wavelength converting materialmay be placed between the LED die and the optical element, e.g., within,over, or under the bonding layer 322. FIG. 5, by way of example,illustrates an LED die 502 mounted to a submount 504 and bonded to anoptical element 506 via bonding layer 508, where a layer of wavelengthconverting material 510 is disposed between the bonding layer 508 andthe optical element 506. The wavelength converting material 510 may bebonded to the bottom surface of the optical element 506 by bonding layer509 prior to or during the bonding the optical element 506 to the LEDdie 502. The wavelength converting material 510 may be, e.g., a phosphorimpregnated glass or wavelength converting ceramic that is formedindependently and then bonded to the LED die 502 and optical element506. In some embodiments, the wavelength converting material 510 may bebonded directly to one or both of the LED die 502 and optical element506. In one embodiment, the optical element 506, LED die 502 andwavelength converting material 510 may be bonded togethersimultaneously. In another embodiment, the wavelength convertingmaterial 510 may be bonded first to the optical element 506 andsubsequently bonded to the LED die 502, e.g., where the bonding layer509 has a higher bonding temperature than the bonding layer 508. Asuitable wavelength converting material, such as a phosphor impregnatedglass, is discussed in more detail in U.S. Ser. No. 10/863,980, filed onJun. 9, 2004, by Paul S. Martin et al., entitled “Semiconductor LightEmitting Device with Pre-Fabricated Wavelength converting member”, whichhas the same assignee as the present application and is incorporatedherein by reference. The wavelength converting material 510 may belarger in area than the die 502, may be the same in area as die 502, ormay be slightly smaller in area than the die 502 as shown. If thewavelength converting material 510 is bonded to the optical element 506before being bonded to die 502, a higher temperature bonding process maybe used than the bonding process used to bond the wavelength convertingmaterial 510 to the LED die 502. Consequently, bonding material 509 maybe a higher temperature bonding material than bonding material 508.

FIG. 6 illustrates another embodiment, similar to the embodiment shownin FIG. 5, except a wavelength converting material 520 is bonded to theLED die 502 (and optionally over the edges of the LED die 502) prior toor during bonding of the optical element 506. Thus, as shown in FIG. 6,the wavelength converting material 520 is placed between the LED die 502and the bonding layer 509.

In another implementation, the coating of wavelength converting materialmay be located over the LED die or dice remotely, e.g., on an envelopeof glass, plastic, epoxy, or silicone with a hollow space between theenvelope and the LED die or dice. If desired, the hollow space may befilled with a material such as silicone or epoxy. In one embodiment, awavelength converting material may be deposited on a standard T1¾ 5 mmLED lamp or a LUXEON lamp from Lumileds, Inc., for example, by spraycoating. This coating may then be tested and corrected until the desiredwavelength spectrum is produced.

FIG. 7 illustrates an array 600 of LEDs 602, which are mounted on aboard 604. The board 604 includes electrical traces 606 that are used toprovide electrical contact to the LEDs 602. The LEDs 602 may be phosphorconverted devices manufactured, e.g., as described above. The LEDs 602may each produce white light with different CCTs. By mixing the whitelight with different CCTs in array 600, a light with a desired CCT maybe produced. If desired, the LEDs 602 may be covered with a transparentelement 608 of e.g., glass, plastic, epoxy, or silicone. The transparentelement 608 may be filled, e.g., with epoxy or silicone, which assiststhe extracting and mixing of the light and to protect the LEDs 602. Itshould be understood that array 600 may include any number of LEDs 602and that if desired, one or more of the LEDs may produce non-whitelight. Moreover, if desired, a plurality of the LEDs 602 may be bondedto a single optical element 603, or one or more of the LEDs 602 may notinclude optical element 603.

As illustrated in FIG. 7, individual or groups of LEDs 602 may beindependently controlled, e.g., by controller 610, which is electricallyconnected to the traces 606 on the board 604. By independentlycontrolling LEDs 602 or groups of LEDs 602, a high color rendering,e.g., over 85, with a constant brightness may be achieved. Further, thewhite points produced by the array 600 may be tunable over a large rangeof CCT, e.g., between 3000K and 6000K. By way of example, a number ofphosphor-converted (PC) blue LEDs that produce white light may be usedin combination with LEDs with different colors, such as blue, cyan,amber and red to produce a light with a desired CCT. As shown in thegraph of FIG. 8, the phosphor converted blue LEDs generates light with abroad spectrum 702 in the green area in combination with a peak in theblue region. The thickness of the phosphor may be tuned to produceapproximately equal peak values for both the green and blue parts of thespectrum. FIG. 9 shows a CIE chromaticity diagram for the spectrum shownin FIG. 8, which illustrates the x and y color coordinates 752 above theblack bodyline 754. Of course, PC LEDs that produce spectra having peaksin other area may be used if desired. Alternatively, if desired, PC LEDsthat produce different spectra, i.e., white light having different CCTsmay be used together.

A majority of the LEDs 602 in the array 600 of FIG. 7 may be PC LEDsthat generate the spectrum shown in FIG. 8. The remaining LEDs 602 shownin FIG. 7 may be colored LEDs, e.g., LEDs that produce blue, cyan, amberand red. The brightness of the colored LEDs may be adjusted bycontroller 610. The combination of fully powered PC LEDs with coloredLEDs generates an approximately continuous spectrum, as illustrated inFIG. 10. FIG. 10 shows a graph with the spectrum 702 from the PC LEDsalong with spectra 704, 706, 708 and 710 from the blue, cyan, amber andred colored LEDs combined to form spectrum 720. As illustrated in theportion of the CIE chromaticity diagram shown in FIG. 11, by varying thebrightness of the colored LEDs, an area that covers part of the blackbody line 764 can be obtained. By way of example, one embodiment thatincluded 29 PC LEDs and 12 color LEDs is capable of producing abrightness of 800 lumen with a color rendering between 85 and 95 and aCCT between 3200K and 5800K. FIG. 12 illustrates a portion of the CIEchromaticity diagram that illustrates variable CCT values for an arrayof 29 PC LEDs and 12 color LEDs. Of course, any number of PC LEDs andcolor LEDs may be used.

Although the present invention is illustrated in connection withspecific embodiments for instructional purposes, the present inventionis not limited thereto. Various adaptations and modifications may bemade without departing from the scope of the invention. Therefore, thespirit and scope of the appended claims should not be limited to theforegoing description.

1. A method comprising: providing a first bonding layer between a lightemitting element and a wavelength converting member; providing a secondbonding layer between the wavelength converting member and an opticalelement, such that the first and second bonding layers are on oppositesides of the wavelength converting member; bonding the light emittingelement to the wavelength converting member with the first bondinglayer; and bonding the wavelength converting member to the opticalelement with the second bonding layer; wherein the bonding of thewavelength converting member to the optical element occurs beforebonding the light emitting element to the wavelength converting member.2. The method of claim 1 wherein at least one of bonding the lightemitting element to the wavelength converting member and bonding thewavelength converting member to the optical element together is done atelevated temperature.
 3. The method of claim 1, wherein the bonding ofthe light emitting element to the wavelength converting member occurs ata first bonding temperature and the bonding of the wavelength convertingmember to the optical element occurs at a second bonding temperature. 4.The method of claim 3, wherein the first bonding temperature and secondbonding temperature are approximately the same.
 5. The method of claim3, wherein the second bonding temperature is higher than the firstbonding temperature.
 6. The method of claim 1, wherein the wavelengthconverting member comprises a wavelength converting ceramic.
 7. Themethod of claim 1, wherein at least one of the first bonding layer andthe second bonding layer comprises an oxide.
 8. The method of claim 1,wherein at least one of the first bonding layer and the second bondinglayer comprises a resin.
 9. The method of claim 1, wherein at least oneof the first bonding layer and the second bonding layer comprises asilicone.
 10. The method of claim 1, wherein at least one of the firstbonding layer and the second bonding layer includes a modified siloxane.11. The method of claim 1, wherein the light emitting element is mountedon a submount.
 12. A method comprising: providing a first bonding layerbetween a light emitting element and a wavelength converting member;providing a second bonding layer between the wavelength convertingmember and an optical element, such that the first and second bondinglayers are on opposite sides of the wavelength converting member;bonding the light emitting element to the wavelength converting memberwith the first bonding layer; and bonding the wavelength convertingmember to the optical element with the second bonding layer; wherein thebonding of the light emitting element to the wavelength convertingmember and the bonding of the wavelength converting member to theoptical element occur at approximately the same time.
 13. A methodcomprising: providing a first bonding layer between a light emittingelement and a wavelength converting member; providing a second bondinglayer between the wavelength converting member and an optical element,such that the first and second bonding lavers are on opposite sides ofthe wavelength converting member; bonding the light emitting element tothe wavelength converting member with the first bonding layer; andbonding the wavelength converting member to the optical element with thesecond bonding layer; wherein the wavelength converting member comprisesa corrected wavelength converting member, the corrected wavelengthconverting member is corrected to have an amount of wavelengthconverting material that is different than the amount of wavelengthconverting material initially coupled to the semiconductor lightemitting element, the amount of wavelength converting material in thecorrected wavelength converting member is sufficient to produce adesired wavelength spectrum.
 14. The method of claim 13 wherein at leastone of bonding the light emitting element to the wavelength convertingmember and bonding the wavelength converting member to the opticalelement is done at elevated temperature.
 15. The method of claim 13,wherein the bonding of the light emitting element to the wavelengthconverting member and the bonding of the wavelength converting member tothe optical element occur at approximately the same time.
 16. The methodof claim 13, wherein the bonding of the wavelength converting member tothe optical element occurs before bonding the light emitting element tothe wavelength converting member.
 17. The method of claim 13, whereinthe bonding of the light emitting element to the wavelength convertingmember occurs at a first bonding temperature and the bonding of thewavelength converting member to the optical element occurs at a secondbonding temperature.
 18. The method of claim 17, wherein the firstbonding temperature and second bonding temperature are approximately thesame.
 19. The method of claim 17, wherein the second bonding temperatureis higher than the first bonding temperature.
 20. The method of claim13, wherein the wavelength converting member comprises a wavelengthconverting ceramic.